1. Field of the Invention
This invention relates generally to light boxes and illuminators incorporating means for viewing transparent and translucent media and more particularly to such devices for viewing x-ray film, photographic film transparencies, and the like.
2. Description of the Prior Art
Since the use of x-ray photography has become commonplace in hospitals and medical clinics, illuminating screen devices have been developed for display and close analysis of the developed film. Typically, these illuminators use either two or four fifteen-watt, for example, fluorescent light tubes, with one Class P ballast being employed for each two light tubes. It is desirable, however, in film illuminators of this kind, to concentrate a maximum amount of evenly distributed light, measured in candle light, within a minimum amount of space, say fourteen inches by seventeen inches in area or less. The combination of fluorescent tubes and associated ballast concentrated in a small volume generates a large amount of heat, which can, dependent on volume and the amount of use, cause ballast to approach a certain limit temperature. A limit temperature for the type of ballast normally used for this application is preset. When this limit temperature is reached, the ballast will cut off, or "cycle", until the ballast and light tubes cool sufficiently to permit the illuminator to relight. This often can take from five to twenty minutes, during which period the light box system is inoperative. When an illuminator cycles in this fashion in a frequent or consistent manner, a user tends to consider the unit as "broken" and demands repair or replacement from the manufacturer. Thus, there is a need to better cool such film illuminators in order to prevent the overheating problems, without significantly introducing higher costs. Furthermore, designs should be such that the illuminators can be made in different sizes without requiring additional tooling or special parts.
Another difficulty encountered with film illuminators commonly employed is in mounting the unit. Typically, film illuminators are either wall mounted or recessed into a wall. In the latter approach film illuminators are installed so that a majority of the depth of the unit is inside a wall. This technique generally is employed only during new construction or remodeling of existing facilities. The less expensive and more common manner of installing a film illuminator is by hanging the unit on the exterior surface of an office or laboratory wall. This can be done by placing screws in the wall at the desired location and subsequently hanging the unit on the screws by use of "key-hole slots" prepunched into the back of the illuminator enclosure. Nevertheless, this mounting has been a major source of complaint from installers as being time consuming, awkward, and in many cases requiring partial disassembly of the illuminator unit in order to insure proper installation. Frequently, two or more people are required to install such a unit.
The mounting techniques, as discussed above, cause additional problems with heat disbursement as well. Heat from prior film illuminators is transferred both outwardly toward the viewer and also towards a back plate of the unit enclosure. With modern wall construction methods, however, the wall acts as a non-conductive heat barrier. That is, heat is trapped in the illuminator enclosure, and as the heat rises, the ballast overheats and cycling results. In addition, much of the heat is forced to disperse through the viewing or operating area or surface of the illuminator, creating unnecessary user discomfort.